The invention relates to a grounding contact for the transfer of currents between fixed vehicle elements of a rail vehicle, in particular an electric, diesel-electric or diesel-hydraulic locomotive or of a self-propelled or long-distance vehicle, and its rotating wheel axle, consisting of at least one contact element, acted upon by a pressure in the direction toward the wheel axle. The contact element rests on a contact surface which originates indirectly or directly at the wheel axle and in particular is made of a carbon material or contains the same.
It is possible to return work and/or signal currents of rail vehicles to the rail, and thus to the energy source, via wheel axles and axle wheels. The transfer from the fixed vehicle elements to the rotating axles is performed by means of special current bridges, which are usually called reverse current/grounding contacts.
The rolling bearings of the axles can be located in the useful current circuit or the parasitic current circuit. To protect them against current flow and therefore against destruction, the reverse flow/grounding contact must form a low- impedance bridge. Current flow through the bearing starts at a voltage present at the bearing of, for example, 0.5 to 1 V (fritt voltage). Together with a rapidly increasing amount of current, the value of the transition voltage subsequently drops to approximately 0.5 V.
Reverse current/signal current/grounding contacts should make a good and secure electrical connection between the reverse current connection on the vehicle and the wheel axle over a defined current pith in all operating situations of the vehicle. Furthermore, it must be assured, in particular in the course of a signal transmission, that a constant transition resistance is present.
In connection with a grounding contact known from DE-OS 1 953 043, a carbon brush is seated, spring-loaded and not rotatable, in a housing originating at an axle of an electrical rail vehicle, which is supported in respect to a rotating contact disk. In this case the carbon brush can either be pressed against a contact plate by means of a pressure spring, or the plate can be pushed against the carbon brush by means of a tension spring. When using a pressure spring, it can possibly originate at a disk which is directly connected with the axle.
A cleaning block is known from DD 81 136, which is not intended as a grounding contact and which can be pressed against the running surface of the wheel of a rail vehicle by means of a hydraulic or pneumatic cylinder.
An electrical rail vehicle with a rubber-sprung driving wheel is known from CH 176 524. In this case the work current is derived via a carbon brush which is pressed against a wheel tire in such a way that the carbon brush simultaneously acts as cleaning block for the running surface of the wheel tire.
A grounding contact of the type mentioned at the outset can be taken from EP 0 582 888 A1. There the contact surface on which the carbon brush is supported consists of carbon material or contains the same. By means of this the advantage of a reduction of wear results in contrast to other grounding contacts.
The instant invention is based on the object of further developing a grounding contact of the type described at the outset in such a way, that low maintenance is achieved along with small structural size and low weight, wherein it should be simultaneously assured that the contact element, such as a carbon brush or carbon brushes, rests or rest flat against the contact surface to the required extent.
The object is attained in accordance with the invention in that
the at least one contact element is acted upon by the pressure of a disk-shaped device filled with a fluid or a flowable material, PA1 on the contact element side the device is delimited by a flexible element, which rests flat against the contact element, PA1 a pressure plate element, which can be charged by means of a spring tension in the direction toward the contact element acts on the side of the device remote from the contact element.
By means of these steps inaccuracies can be compensated without problems, wherein it is simultaneously assured that the contact element, such as a carbon brush or carbon brushes, rests flat against the contact surface to the required extent. Because the device transferring the pressure can be filled with a fluid or a flowable material, i.e. fulfills the function of a cushion, a small structural size is possible. Regardless of the number of contact elements, such as carbon brushes, supported on the contact surface, only a single pressure-exerting device, such as a cushion, is necessary, so that a structural simplification results, along with the simultaneous increase of the required maintenance intervals.
The invention provides in particular that the side remote from the contact element has a further flexible element on which the pressure plate element acts.
To assure a structurally simple construction, it is provided that the device has a circumferential frame, U-shaped in cross section, on the inside of which a support ring is disposed, between which and the frame the flexible elements are fixed in place, such as clamped.
Fluids with high compressibility are particularly considered, such as liquids. In this case glycol is particularly to be preferred. Other suitable, environmentally friendly flowable materials as also suitable. Brake fluid, grainy material, such as sand, can be cited as examples.
In order to fill the device in simple steps, a further suggestion of the invention provides that the frame has a filler opening, which can be closed by means of a ball on the inside and by means of a closing element, such as a screw, on the outside.
In general, it should be possible to fill the interior of the device, which is delimited at least on the side of the contact element by the flexible element, via a flap valve cut into the frame.
To realize a simple structure of the frame itself it is provided that it is composed of clamping rings, which are L-shaped in cross section. The frame itself can be received in a hollow- cylindrical holder, from which a yoke originates at the side remote from the contact element, which is a support for the spring element, such as a helical spring, acting on the pressure plate element.
The contact element itself can consist of segments separated by spacer elements which, viewed from the direction of the contact surface, have a triangular shape. Even though this is considered to be a preferred embodiment of the contact element, other arrangements can also be employed for being installed in a grounding contact in accordance with the invention.